This research project focuses on identifying and characterizing plasma membrane proteins in the rod photoreceptor outer segment. Little is known about these proteins, despite their importance in controlling light-dependent changes in sodium conductance, as well as other functions in phototransduction. The development of a new density gradient centrifugation procedure for purifying intact rod outer segments substantially free of contaminants has made it possible to successfully label minor proteins on the surface. For more conclusive identification of surface proteins, several different techniques will be employed. These include: (1) iodination and identification of labeled proteins on autoradiograms; (2) isolation of the plasma membrane by density gradient centrifugation; and (3) obtaining monoclonal antibodies to surface proteins. These antibodies will be used to probe the function of surface molecules, to isolate them, and to map their location within the rod outer segment. Monoclonal antibodies to surface proteins will be powerful tools because they are more specific than probes now available for localization or functional studies. Since some disease processes specifically may involve surface proteins (e.g. retinitis pigmentosa), elucidation of the functions of the cell surface may further our understanding of these disease processes as well as the basic process of phototransduction.